In conventional melt spinning processes, in particular those used for polyesters, the filaments are extruded/drawn at high temperatures, close to 300° C. These filaments or fibers are cooled down to their glass transition temperature (TG) under stretched conditions using cold or conditioned air to get the desired rheological properties.
Generally, the extruded filaments are quenched by blowing conditioned air from a screen in a direction perpendicular to a path of the drawn filaments. The cold or conditioned air temperature is typically kept between 18° C. to 25° C. and is blown at a speed of about 0.5 to 1 m/s by means known in the art, for example, a blower. The temperature and speed of the conditioned air is adjusted within the range depending upon the denier to be spun. The process is commonly known as cross flow quench system.
The cross-flow quench system is the most widely used quenching system. However, in a typical cross-flow quench system the filaments reach the desired temperature at which they can safely be spun by the time they reach half of the screen length; thereafter, the cold air gets wasted.
There have been systems known in art that have tried to save on the chilling cost of air for quenching purposes. For example, in some cross-flow quench systems, ambient air is used to cool off the filaments to certain length before the same can be further cooled down to the desired temperature by using less amount of conditioned air. However, the refrigeration or conditioning cost associated with quenching systems is still substantial and needs further correction in the state-of-the-art.
Even in systems that use a combination of ambient air and cold air in step-wise quenching, there is no precise estimation of a location from where the conditioned air should be blown across the filaments in order to have a consistent lot of spun fiber with, the desired properties and with minimum requirement of conditioned air. Thus, with the existing quenching systems, the quality and/or rheological properties of the end product is hard to maintain.